This application is based on Japanese Patent Application No. 2002-171565 filed on Jun. 12, 2002, the disclosure of which is incorporated herein by reference.
The present invention relates to a vehicle air conditioner having a hot gas heating function using an interior heat exchanger (evaporator) as a radiator by directly introducing a gas refrigerant (hot gas) discharged from a compressor into the interior heat exchanger. The present invention relates particularly to a system in which condensed water is prevented from evaporating in the interior heat exchanger and from fogging a vehicle windshield in a heating mode.
In a conventional vehicle air conditioner, hot water (i.e., engine cooling water) is circulated in a heating heat exchanger during a heating operation in winter to heat air in the heating heat exchanger by using the hot water as a heat source. In this case, when the hot water temperature is low, the temperature of air to be blown into a passenger compartment is lowered and thus may be insufficient for a heating capacity.
Thus, JP-A No. H5-272817 proposes a vehicle air conditioner which has a heating function by using a hot gas heater cycle. When the hot water temperature is lower than a predetermined value as just after the start-up of an engine, gas refrigerant (or hot gas) discharged from a compressor is introduced into an interior heat exchanger (evaporator) while bypassing a condenser to release the heat from the gas refrigerant to the air in the interior heat exchanger to obtain an auxiliary heating function. That is, in the above conventional vehicle air conditioner, one interior heat exchanger disposed in an air conditioner case is selectively used as a cooler in a cooling mode and as a radiator in a heating mode.
By the way, in the vehicle air conditioner, an inside air mode may be set to prevent contaminated outside air from being introduced during the heating mode in winter. In this case, it is necessary for the evaporator to cool and dehumidify the air to prevent the windshield from fogging. Accordingly, until an outside air temperature drops to 0xc2x0 C., the refrigerating cycle may be used in the cooling mode.
After the refrigerating cycle is operated at an outside air temperature of about 0xc2x0 C. with the cooling mode to prevent the fogging of the windshield, the refrigerating cycle may be switched to the hot gas heater cycle (heating mode) to increase the heating capacity. Moreover, after the refrigerating cycle is operated with the cooling mode and then is stopped at once and is started with the hot gas heating cycle (heating mode).
In the above case, condensed water generated in the cooling mode of the refrigerating cycle remains on the surface of the interior heat exchanger. Thus, if the refrigerating cycle is started in the heating mode, the interior heat exchanger functions as the radiator of the gas refrigerant to rapidly increase the temperature of the interior heat exchanger. Accordingly, the condensed water on the surface of the interior heat exchanger evaporates, and air having a high humidify is blown into the passenger compartment, so that the vehicle windshield is fogged.
Moreover, the condensed water once generated on the interior heat exchanger by the operation of the cooling mode does not easily evaporate at a low outside air temperature in winter and may remain for a long time. Thus, even not just after switching from the cooling mode to the heating mode, the vehicle windshield may be fogged by starting the heating mode of the refrigerating cycle.
Thus, the present applicant proposed, in JP-A No. 2000-219034 (corresponding to U.S. Pat. No. 6,311,505), an invention of aiming to prevent the condensed water in the interior heat exchanger from evaporating and fogging the vehicle windshield in the heating mode in the vehicle air conditioner having the hot gas heating function.
In this related art, a physical quantity relating to the temperature of the windshield and the inside air humidity in the vicinity of the vehicle windshield are detected and it is determined based on this physical quantity whether or not the windshield is in the state of fogging. When it is determined that the vehicle windshield is in the state of fogging, the refrigerating cycle is controlled so as to suppress the temperature of the interior heat exchanger. More specifically, the temperature of the air blown out of the interior heat exchanger is controlled to suppress the evaporation of the condensed water in the interior heat exchanger to thereby prevent the vehicle windshield from fogging.
However, in an automatic control system of this air conditioner, when the temperature of the engine-cooling water is low in the winter, warm-up control is performed for preventing cool air from being blown into the passenger compartment. In the warm-up control, even when a blower switch is turned on, a stop state of a blower is maintained until the temperature of the water in the engine is increased to a predetermined temperature (e.g., 30xc2x0). Therefore, when the hot gas heating mode is set and the hot gas heater cycle is operated while the stop state of the blower is maintained in the warm-up control, the temperature of the interior heat exchanger is rapidly increased due to high-temperature refrigerant discharged from the compressor because air is not blown to the interior heat exchanger. As a result, in this air conditioner, it is necessary to stop the operation of the hot gas heating mode while the blower stops. Therefore, in this case, it is difficult to obtain a temperature increasing effect of water in the engine, due to the operation of the hot gas heating mode.
In view of the above-described problems, it is an object of the present invention to provide a vehicle air conditioner that can perform a hot gas heating mode while preventing a vehicle windshield from fogging, even when a blower for blowing air stops.
According to the present invention, an air conditioner includes a blower disposed in an air conditioning case for blowing air, a refrigerant cycle with a hot gas heating function, and a control unit for controlling operation of the refrigerant cycle. The refrigerant cycle system includes a compressor for compressing refrigerant, an exterior heat exchanger disposed outside the air conditioning case, a pressure reducing device for decompressing refrigerant, an interior heat exchanger disposed inside the air conditioning case and a hot gas bypass passage through which refrigerant discharged from the compressor is directly introduced into the interior heat exchanger while bypassing the exterior heat exchanger. The refrigerant cycle system is constructed to switch a cooling refrigerant cycle where refrigerant discharged from the compressor is returned to the compressor through the exterior heat exchanger, the pressure reducing device and the interior heat exchanger, and a hot gas heater cycle where the refrigerant discharged from the compressor is directly introduced to the interior heat exchanger through the hot gas bypass passage. Further, the control unit controls operation of the refrigerant cycle system to set a cooling mode for cooling air in the interior heat exchanger by using the cooling refrigerant cycle, and a hot gas heating mode for heating air in the interior heat exchanger by using the hot gas heater cycle. In the air conditioner, control means of the control unit performs operation of the heating mode when determining means of the control unit determines that the interior heat exchanger does not have the quantity of retained water when the heating mode is set while operation of the blower stops, and stops the operation of the heating mode when the determining means determines that the interior heat exchanger has the quantity of retained water when the heating mode is set while operation of the blower stops.
When the operation of the blower stops, because air is not blown into the interior heat exchanger, the temperature of air from the interior heat exchanger is greatly increased as compared with a case where the blower operates. However, when the interior heat exchanger does not have the quantity of retained water, the windshield is not fogged even when the heating mode is performed. Accordingly, in the present invention, when the determining means determines that the interior heat exchanger does not have the quantity of retained water while the operation of the blower stops, the operation of the heating mode is continued while a heating capacity control based on temperature of air from the interior heat exchanger is not performed. Thus, even when the blower is stopped in the heating mode, compressor-driving load of the engine increases, the water temperature in the vehicle engine increases, and heating capacity of a hot-water type heat exchanger can be rapidly increased. On the other hand, because the operation of the heating mode is stopped when the interior heat exchanger has the quantity of retained water, it can prevent the windshield from being fogged.
Further, when the determining means determines that the interior heat exchanger does not have the quantity of retained water when the heating mode is set while the blower operates, the control means performs operation of the heating mode. Accordingly, when it is unnecessary to perform the defogging control, the heating capacity in the heating mode can be effectively improved without restricting the temperature of air blown from the interior heat exchanger. On the other hand, when the determining means determines that the interior heat exchanger has the quantity of retained water when the heating mode is set while the blower operates, the control means controls temperature of air blown out of the interior heat exchanger to a range lower than a dew point even when air blown out of the air conditioning case is cooled by a vehicle windshield. Therefore, it can prevent the windshield from being fogged in the operation of the blower. For example, the quantity of retained water is calculated based on at least a quantity of condensed water in the interior heat exchanger in the cooling mode, a quantity of evaporation of condensed water in the interior heat exchanger in the heating mode, and a quantity of condensed water discharged from a discharge port of the air conditioning case in an uncontrolled mode where the compressor is in a stop state. Alternatively, the quantity of condensed water is calculated at least based on an elapsed time after a stop of operation of the cooling mode.